Flat panel display devices, such as liquid crystal displays (LCD), organic electroluminescent displays (OELD) and plasma display panels (PDP) have attracted public attention as good alternatives to conventional display devices such as heavy and bulky cathode ray tube (CRT) devices.
Thin film transistors (TFT) used in flat panel displays require high speed operation in response to given signals and uniformity over the entire substrate. To create TFTs having these characteristics, it is very important to control the characteristics of the TFT semiconductor layer.
Techniques used to crystallize an amorphous silicon layer to form a polysilicon layer typically include solid phase crystallization, excimer laser crystallization, metal induced crystallization (MIC), and metal induced lateral crystallization (MILC). Solid phase crystallization involves heat-treating and crystallizing an amorphous silicon layer for several hours to tens of hours at the glass transition temperature, i.e. at a temperature of less than about 700° C. This process creates a substrate on which a TFT is formed. Excimer laser crystallization involves scanning an amorphous silicon layer with an excimer laser and heating the amorphous silicon layer at a high temperature for a very short period of time to crystallize the amorphous silicon layer.
Solid phase crystallization is disadvantageous because the substrate is exposed to a high temperature for a long period of time and may therefore be easily damaged. Excimer laser crystallization is also disadvantageous because the required excimer laser and maintenance fees are expensive. MIC and MILC are also disadvantageous because both processes require a long period of time to crystallize the polysilicon layer.